A series of experiments are proposed to examine whether principles of behavioral economics operate in studies of drug preference with humans. In all of the studies, healthy volunteers will perform on a concurrent choice task for a drug and a non-drug reinforcer. The major dependent measure in the studies is the amount of drug reinforcement that subjects obtain during the task. In the first series of studies, we will examine whether drug choice can be altered (i.e., reduced) by the availability and magnitude (i.e., size) of an alternative non-drug reinforcer or by its own availability and magnitude. In the second series of studies, we will determine whether abstinence from a drug (caffeine, nicotine) in individuals who are physically dependent on the drug decreases the elasticity of demand of the drug. In the third series of studies, we will examine relative demand for a drug reinforcer (cigarettes) compared to a non-drug reinforcer (money), when subjects have to stay in the laboratory setting after a session in which they can smoke only the cigarettes that they earned during the task (analogous to a closed economy) as opposed to a situation in which they are allowed to leave the laboratory setting immediately after the task is completed (analogous to an open economy). In the last study, subjects will be pretreated with different doses of alcohol prior to sessions in which they can work for cigarettes or for money to determine if a drug that is typically co-administered with -cigarettes, alcohol, decreases the elasticity of demand of cigarettes. In short, the focus of this grant application is to extend the generality of behavioral economic principles validated in the animal laboratory to the human milieu, with particular reference to human drug use.